Plunger pump

ABSTRACT

A plunger pump includes a pump body, a pump head attached to a tip end portion of the pump body, the pump head including a pump chamber, an inlet path and an outlet path, a plunger that slides in an axial direction along the inner wall of the pump chamber, and a ring-shaped plunger seal for preventing fluid leakage from the pump chamber to the pump body. The plunger seal is arranged between the pump chamber and the pump body with a front surface facing the pump chamber and a back surface facing the pump body, includes a penetration hole from the front surface to the back surface, and holds the plunger in a slidable manner with the inner wall of the penetration hole. The plunger seal includes a ring-shaped hollow portion surrounding the penetration hole, the hollow portion communicating with a back surface side of the plunger seal and not communicating with a front surface side of the plunger seal. An elastic member for expanding the hollow portion in a radial direction of the plunger by an elastic force is provided inside the hollow portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plunger pump which is a type ofdelivery pump used for delivering a mobile phase of a liquidchromatograph, for example, and which performs delivery by sliding aplunger inside a pump chamber provided in a pump head.

2. Description of the Related Art

A general plunger pump (see Japanese Patent Laid-open Publication No.2001-254686) will be described using FIG. 3.

A pump head 38 is attached at a tip end of a pump body 30 across acleaning chamber 44 for cleaning a plunger 33. A crosshead 34 thatreciprocates in one direction by a cam mechanism (not shown) and aspring 36 is accommodated within the pump body 30, and a plunger 33 isattached at the tip end of the crosshead 34. A tip end portion of theplunger 33 is inserted into a pump chamber 38 a provided inside the pumphead 38, and slides inside the pump chamber 38 a along the inner wall ofthe pump chamber 38 a.

An inlet path 38 b and an outlet path 38 c communicating with the pumpchamber 38 a are provided to the pump head 38. Check valves 39 a and 39b that open or close according to the pressure inside the pump chamber38 a are provided to the inlet path 38 b and the outlet path 38 c. Whenthe plunger 33 is moved to the suction side (the right side in thedrawing), the check valve 39 a opens and fluid is drawn into the pumpchamber 38 a from the inlet path 38 b, and when the plunger 33 moves tothe discharge side (the left side in the drawing), the check valve 39 bopens and the fluid inside the pump chamber 39 a is discharged from theoutlet path 38 c.

A concave portion 40 communicating with the pump chamber 38 a isprovided on a surface of the pump head 38, on the side of the pump body30. A plunger seal 42 which the plunger 33 penetrates and which holdsthe plunger 33 in a slidable manner is embedded in the concave portion40, and a backup ring 43 is inserted on the back surface side of theplunger seal 42 (on the side of the surface on the pump body 30 side).The plunger seal 42 is for preventing the fluid from the pump chamber 38a from leaking to the side of the pump body 30. A cleaning seal 46 forpreventing leakage of cleaning fluid is attached to the cleaning chamber44.

The plunger seal 42 has a ring-shaped concave portion 42 a provided onthe front surface facing the pump chamber 38 a, and is structured toexpand the concave portion 42 a when the delivery pressure is high bystoring the fluid which has leaked from the pump chamber 38 a and toimprove the sealing performance of the plunger seal 42. Moreover, aring-shaped metal spring 50 is inserted into the concave portion 42 a,and the sealing performance of the plunger seal 42 is further improvedby the elastic force of the metal spring 50.

As described above, the fluid which has leaked from the pump chamber 38a is stored in the concave portion 42 a on the front surface of theplunger seal 42, and thus, in the cases which the fluid to be deliveredis highly corrosive to metal, the metal spring 50 inserted into theconcave portion 42 a is corroded. Accordingly, under a condition wherethe delivery pressure is high, delivery of fluid highly corrosive tometal could not be performed. Also, in the case of using the plungerpump to deliver a mobile phase in a liquid chromatograph, even if themobile phase is not fluid which is highly corrosive to metal, metal ionsmay dissolve in the mobile phase by the metal spring 50 coming intocontact with the mobile phase, and a chemical reaction with a functionalgroup or an analytical sample in a separation column may occur, possiblynegatively affecting the analysis result.

SUMMARY OF THE INVENTION

The present invention aims to provide a plunger pump capable ofdelivering even fluid that is corrosive to metal at a high pressure.

A plunger pump, which is the target of the present invention, includes apump body, a pump head attached to a tip end portion of the pump body,the pump head including a pump chamber, and an inlet path and an outletpath communicating with the pump chamber, a plunger whose base end isheld inside the pump body and whose tip end is inserted into the pumpchamber, the plunger being adapted to slide in an axial direction alongan inner wall of the pump chamber, and a ring-shaped plunger sealarranged between the pump chamber and the pump body with a front surfacefacing the pump chamber and a back surface facing the pump body, theplunger seal including a penetration hole from the front surface to theback surface, and holding the plunger in a slidable manner with an innerwall of the penetration hole and preventing fluid leakage from the pumpchamber to the pump body.

In the present invention, according to such a plunger pump, the plungerseal includes a ring-shaped hollow portion surrounding the penetrationhole, an elastic member for expanding the hollow portion in a radialdirection of the plunger by an elastic force is provided inside thehollow portion, the hollow portion communicates with a back surface sideof the plunger seal and does not communicate with a front surface side,and a metal elastic member is not provided at a position that comes intocontact, at the front surface side of the plunger seal, with fluid thatis delivered.

According to the plunger pump of the present invention, since a metalelastic member is not attached to the front surface side of the plungerseal, the metal elastic member is not corroded by the fluid from thepump chamber, or metal ions are not dissolved due to the fluid from thepump chamber coming into contact with the metal elastic member.Moreover, the plunger seal includes the ring-shaped hollow portionsurrounding the penetration hole, an elastic member for expanding thehollow portion in a radial direction of the plunger by an elastic forceis provided inside the hollow portion, and the hollow portioncommunicates with the back surface side of the plunger seal and does notcommunicate with the front surface side, and thus, the sealingperformance of the plunger seal may be improved by the elastic force ofthe elastic member, and the pressure resistance may be increased. Sincethe hollow portion provided with the elastic member is not communicatedwith the front surface side, even if the elastic member is made ofmetal, it does not come into contact with the fluid from the pumpchamber, and fluid which is corrosive to metal may be delivered at ahigh pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional diagram showing a pump body and a pump headaccording to an example embodiment of a plunger pump.

FIG. 1B is a cross-sectional diagram of the pump head.

FIG. 2 is a cross-sectional diagram of a pump head according to anotherexample embodiment of the plunger pump.

FIG. 3A is a cross-sectional diagram showing a pump body and a pump headof a conventional plunger pump.

FIG. 3B is a cross-sectional diagram showing the pump head.

DETAILED DESCRIPTION OF THE INVENTION

In another embodiment of the plunger pump, the elastic member isring-shaped surrounding the penetration hole along the ring shape of thehollow portion. An example of the elastic member is a coil spring thatis curved into a ring shape.

In another embodiment of the plunger pump, a ring-shaped pressure spaceis preferably provided, the pressure space communicating with the frontsurface side of the plunger seal and being adapted to press, in theradial direction of the plunger, the plunger seal by the pressure causedby the entering of fluid which has been delivered. Then, the sealingperformance of the plunger seal may be improved at the front surfaceside of the plunger seal, using fluid from the pump chamber, and thepressure resistance of the plunger seal may be further increased.

The pressure space is provided inside the plunger seal, and preferablyexpands in the radial direction of the plunger with the increase in theinternal pressure and presses the plunger seal against the plunger andthe inner wall surface of the pump head. Then, the sealing between theplunger seal and the plunger, and the sealing between the plunger sealand the inner wall surface of the pump head may be improved using thefluid from the pump chamber.

Moreover, the pressure space may also be a gap provided between theouter surface of the plunger seal and the inner wall surface of the pumphead. Also in this case, the sealing between the plunger seal and theplunger may be improved using the fluid from the pump chamber.

An example embodiment of a plunger pump will be described using FIG. 1.

A plunger pump includes a pump body 2, and a pump head 8 attached at atip end of the pump body 2. A cleaning chamber 14 is provided betweenthe pump body 2 and the pump head 8. A crosshead 4 is accommodatedinside the pump body 2 in a movable manner. The crosshead 4 is biased ina direction away from the pump head 8 (in the right direction in thedrawing) by an elastic body 6 such as a spring, and the crosshead 4reciprocates along one direction (the left and right direction in thedrawing) inside the pump body 2 by a cam mechanism (not shown) providedon a base end portion side of the crosshead 4 and the elastic force ofthe elastic body 6.

A base end portion of the plunger 3 is attached at a tip end of thecrosshead 4. A tip end portion of the plunger 3 penetrates the cleaningchamber 14, and is inserted into a pump chamber 8 a provided inside thepump head 8. With the crosshead 4 being driven, the plunger 3reciprocates along the axial direction thereof, and the tip end portionof the plunger 3 slides along the wall surface of the pump chamber 8 a.The pump head 8 includes an inlet path 8 b for drawing fluid into thepump chamber 8 a, and an outlet path 8 c for discharging the fluid fromthe pump chamber 8 a. Check valves 9 a and 9 b are provided on the inletpath 8 b and the outlet path 8 c, respectively, so as to prevent reverseflow.

A plunger seal attaching portion 10 is provided on a surface of the pumphead 8, on the side of the pump body 2. The plunger seal attachingportion 10 is a concave portion that is coaxial with the pump chamber 8a and has an inner diameter greater than the inner diameter of the pumpchamber 8 a, and its bottom surface communicates with the pump chamber 8a. A plunger seal 12 is inserted into the plunger seal attaching portion10, and a backup ring 13 is inserted on the back surface side of theplunger seal 12. The plunger seal 12 has a penetration hole where theplunger 3 is to penetrate, and holds the plunger 3 in a slidable mannerand prevents the fluid from the pump chamber 8 a from leaking to theside of the pump body 2. The backup ring 13 is supported by a surface,on the side of the pump head 3, of the cleaning chamber 14, and servesthe role of pressing the plunger seal 12 to the side of the pump chamber8 a.

The cleaning chamber 14 includes a path through which cleaning fluidflows, and a space where the outer circumferential surface of thepenetrating plunger 3 is cleaned by the cleaning fluid. A cleaning seal16 is provided at a portion in the internal space of the cleaningchamber 14 where the plunger 3 is to be inserted, the cleaning seal 16holding the outer circumferential surface of the plunger 3 in a slidablemanner so as to prevent leakage of the cleaning fluid. The back surfaceof the cleaning seal 16 is supported by a wall surface of the pump body2.

With this delivery pump, when the plunger 3 is driven in the directionaway from the pump chamber 8 a (in the right direction in the drawing),the pressure inside the pump chamber 8 a is reduced, the check valve 9 bis closed, the check valve 9 a is opened, and the fluid is drawn intothe pump chamber 8 a from the inlet path 8 b. On the other hand, whenthe plunger 3 is driven in the direction of insertion into the pumpchamber 8 a (in the left direction in the drawing), the inside of thepump chamber 8 a is pressurized, the check valve 9 a is closed, thecheck valve 9 b is opened, and the fluid is discharged from the pumpchamber 8 a into the outlet path 8 c. Fluid is delivered with thisoperation being performed repeatedly.

The plunger seal 12 is made of an elastic material such as polyethyleneresin. A hollow portion 12 a is provided on the back surface side of theplunger seal 12. The hollow portion 12 a is a ring-shaped hollow spacewhich is open on the back side and is coaxial with the plunger 3. Aring-shaped metal spring (an elastic member) 18 is inserted from theback side into the hollow portion 12 a. The metal spring 18 is forapplying an elastic force in the direction of pressing a part 12 c ofthe plunger seal 12 existing between the metal spring 18 and the plunger3 toward the plunger 3. An example of the metal spring 18 is ring-shapedsurrounding the penetration hole of the plunger seal 12, along the ringshape of the hollow portion 12 a. A concrete example of such a metalspring 18 is a coil spring that is curved into a ring shape.

According to this structure, the sealing between the innercircumferential surface of the plunger seal 12 and the outercircumferential surface of the plunger 3 is increased by the elasticforce of the metal spring 18, and the fluid which has leaked from thepump chamber 8 a may be prevented from reaching the back surface side ofthe plunger seal 12. Since the opening of the hollow portion 12 a is onthe back side, the fluid which has leaked from the pump chamber 8 a doesnot enter the hollow portion 12 a, and the metal spring 18 which isinserted into the hollow portion 12 a does not come into contact withthe fluid which has leaked from the pump chamber 8 a. Thus, the metalspring 18 which improves the sealing performance of the plunger seal 12is not corroded, and metal ions do not dissolve from the metal spring 18into the fluid which is to be delivered. Accordingly, even if the fluidto be delivered is fluid which is corrosive to metal, it may bedelivered under a condition of high pressure where the fluid may leakfrom the pump chamber 8 a to the front surface of the plunger seal 12.

Furthermore, a pressure space 12 b is provided on the front surface ofthe plunger seal 12, the pressure space 12 b being a concave portionwhich is coaxial with the plunger 3. The pressure space 12 b is formedinto a ring shape surrounding the plunger 3. The pressure space 12 bexpands using the increase in the pressure due to the entering of thefluid from the pump chamber 8 a, and improves the sealing between theinner circumferential surface of the plunger seal 12 and the plunger 3,and the sealing between the plunger seal 12 and the innercircumferential surface of the plunger seal attaching portion 10.Accordingly, the fluid which has leaked from the pump chamber 8 a may beeven more prevented from reaching the back surface side of the plungerseal 12.

Additionally, the pressure space 12 b does not necessarily have to beprovided to the plunger seal 12. For example, in the example embodimentin FIG. 2, a gap to be a pressure space is provided between the outersurface of a tip end portion of a plunger seal 22 and the inner wallsurface of a plunger seal attaching portion 20 provided to the pump head8, the pressure inside the gap is increased by the entering of fluidinto the gap from the pump chamber 8 a, and the tip end portion of theplunger seal 22 is pressed toward the plunger 3. A hollow portion 22 ais provided on the back surface side of the plunger seal 22, as in thecase of the plunger seal 12, and a metal spring 24, which is an elasticmember, is inserted into a hollow portion 22 a from the back side. Themetal spring 24 is the same as the metal spring 18 in the exampleembodiment in FIG. 1B. A part 22 c of the plunger seal 22 existingbetween the metal spring 24 and the plunger 3 is pressed toward theplunger 3 by the elastic force of the metal spring 24, and the sealingperformance of the plunger seal 22 is improved. Thus, the fluid whichhas leaked from the pump chamber 8 a is prevented from reaching the backsurface side of the plunger seal 22, and the metal spring 24 may beprevented from coming into contact with the fluid to be delivered.

The invention claimed is:
 1. A plunger pump comprising: a pump body; apump head attached to a tip end portion of the pump body, the pump headincluding a pump chamber, and an inlet path and an outlet pathcommunicating with the pump chamber; a plunger whose base end is heldinside the pump body and whose tip end is inserted into the pumpchamber, the plunger being adapted to slide in an axial direction alongan inner wall of the pump chamber; and a ring-shaped plunger sealarranged between the pump chamber and the pump body with a front surfacefacing the pump chamber and a back surface facing the pump body, theplunger seal including a penetration hole from the front surface to theback surface, and holding the plunger in a slidable manner with an innerwall of the penetration hole and preventing fluid leakage from the pumpchamber to the pump body, wherein the plunger seal includes aring-shaped hollow portion surrounding the penetration hole, the hollowportion communicating with a back surface side of the plunger seal andnot communicating with a front surface side of the plunger seal, and anelastic member for expanding the hollow portion in a radial direction ofthe plunger by an elastic force is provided inside the hollow portion,and wherein a metal member is not provided at a position that comes intocontact, at the front surface side of the plunger seal, with fluid thatis delivered.
 2. The plunger pump according to claim 1, wherein theelastic member has a ring shape surrounding the penetration hole along aring shape of the hollow portion.
 3. The plunger pump according to claim2, wherein the elastic member is a coil spring that is curved into aring shape.
 4. The plunger pump according to claim 1, furthercomprising: a ring-shaped pressure space communicating with the frontsurface side of the plunger seal, the pressure space being adapted topress the plunger seal in the radial direction of the plunger by apressure caused by entering of the fluid which has been delivered. 5.The plunger pump according to claim 4, wherein the pressure space isprovided inside the plunger seal, and is adapted to expand in the radialdirection of the plunger with an increase in an internal pressure of thepressure space and to press the plunger seal against the plunger and aninner wall surface of the pump head.
 6. The plunger pump according toclaim 4, wherein the pressure space is a gap provided between an outersurface of the plunger seal and an inner wall surface of the pump head.